In hypertension, efferent sympathetic activity to post-ganglionic sympathetic nerves and chromaffin cells is increased, contributing to vasoconstriction, sodium retention, and elevations in blood pressure. The chromogranins/secretogranins (chromogranin A [Cga]. Chromogranin B [Cgb]. And secretogranin II [SgII], are a family of acidic proteins found in cores of amine and peptide hormone and neurotransmitter secretory vesicles, such as chromaffin granules and large dense core vesicles of post-ganglionic sympathetic (noradrenergic) axons. Their biologically active fragments act on hormone or neurotransmitter release as well as on target cells at several sites: CgA fragment catestatin inhibits catecholamine release, CgA fragment vasostatin dilates resistance vessels, CgA fragment pancreastatin antagonizes insulin secretion and elevates blood glucose. This proposal develops 3 aims, employing novel targeted photoprotein constructs (luciferase or green fluorescent protein [GFP]) or novel expressed cDNAs, to elucidate how sympathetic outflow changes the composition of catecholamine storage vesicles. In Aim 1, we employ novel transgenic mouse strains, harboring CgA or SgII promoter/luciferase reporters, to probe mechanisms of stimulus/transcription (stimulus/secretion/synthesis) coupling in the sympathoadrenal system in vivo. In Aim 2, we use a series of novel, targeted CgA domain/green fluorescent protein (CgA/EGFP) chimeras to discover information within the primary structure of catecholamine storage vesicle proteins that accounts for their trafficking into the regulated secretory pathway. In Aim 3, we use a novel cDNA expression cloning approach to identify proteins in trans, within the secretory apparatus, which interact with CgA and thereby underlie its trafficking into the regulated secretory pathway. These studies will enhance our understanding of the biosynthesis of catecholamine storage vesicles and the replenishment of their secretory proteins during sympathetic stimulation. Finally, these photoprotein and cDNA reagents can be widely employed by other investigators in elucidating biosynthetic, trafficking, and ion flux events in the sympathochromaffin system.